A background art example of a method for unwinding of yarns from a creel is the over-end-take-off (OETO) method. The OETO method allows for continuous operation of the unwinding process since the terminating end of the yarn of an active package is attached to the leading end of the yarn of a standby package. In the OETO method, after the active package is fully exhausted, the standby package becomes the active package. However, a drawback of the OETO method is that unacceptable yarn tension variations can occur during the unwinding process.
A background art example of a system and apparatus that implements the OETO method was disclosed in Research Disclosure, p. 729, November 1995, item #37922. In particular, the disclosure describes an OETO system that elastomeric fibers are passed through before being fed to a manufacturing line. The OETO system of the disclosure has a rack structure that holds the creels of active packages and standby packages, a relaxation section and motor driven nip rolls. The relaxation section is located between an active package and the nip rolls of the OETO system. The relaxation section helps to suppress the unacceptable yarn tension variations discussed above by providing some slack in the yarn being unwound.
However, background art OETO systems that include such a relaxation section have problems with fibers or yarns that exhibit high levels of tack (i.e., yarns having particularly high cohesive forces). Moreover, yarns with high levels of tack also display unusually high variations in frictional forces and yarn tension levels as the active package is unwound from the creel.
In addition, the slack in the yarn provided by the relaxation section can vary, and excess yarn can be unwound from the active package. This excess yarn can be drawn into the nip rolls and wound upon itself leading to entanglement or breakage of the yarn. Use of yarns with high levels of tack further contributes to the possibility of the excess yarn adhering to itself and to the nip rolls. The entanglement or breakage of yarns during the unwinding process requires the manufacturing line to be stopped, delays the unwinding process and increases the cost of manufacturing.
Background art OETO apparatus are typically configured such that the yarn horizontally traverses the relaxation section. In this configuration, the yarn travels through nip rolls with axes that are vertical. However, with such a vertical configuration for the axes of the nip rolls, the yarn located in the relaxation section between the active package and the nip rolls tends to sag. As a result, the yarn position on the nip rolls can become unstable, and interference and entanglement can occur between adjacent yarns. Each of these problems would require the manufacturing line to be stopped.
Furthermore, some manufacturing applications (e.g., diaper manufacturing) require the use of as-spun fiber that is substantially finish-free. Such finish-free yarns also exhibit the problems associated with high levels of tack discussed above.
The problems discussed above make applying OETO methods and apparatus particularly difficult when processing yarn with a high level of tack. Background art OETO apparatus have attempted to address these problems in the unwinding process by: (1) using yarns with anti-tack additives applied prior to winding; and/or (2) using rewound packages, where an active package is unwound and then rewound on a different creel to create a rewound package. Both of these approaches add additional expense to the manufacturing and unwinding processes.
As a result of the problems discussed above, OETO apparatus of the background art have been designed to take into account the difficulties due to the relaxation section, high levels of tack and breakage in yarns unwound with the OETO method. As an example, U.S. Pat. No. 6,676,054 (Heaney et al.) discloses an OETO method and apparatus for unwinding elastomeric fiber packages with high levels of tack from a package. In particular, the OETO apparatus of Heaney et al. requires that a minimum distance exists between a fiber guide and the fiber package. In accordance with Heaney et al., minimum distances less than 0.41 meter can result in undesirably large tension variations. These variations can cause process control difficulties and can also lead to yarn breakages. Further, in accordance to Heaney et al, distances longer than 0.91 meter make the unwinding equipment less compact and ergonometrically less favorable. As the level of tack exhibited by the fiber increases, the minimum allowable distance, d, increases. For yams with tack levels greater than about 2 grams and less than about 7.5 grams, d is preferably at least about 0.41 meter; and for fibers with tack levels greater than about 7.5 grams, d is preferably at least about 0.71 meter.
However, due to such minimum distance and other requirements for high tack yarns, OETO apparatus typically requires a frame with a large footprint that can take up significant floor space in a manufacturing environment.
Therefore, there is a need in the art for an OETO apparatus for unwinding yarns with high levels of tack that avoids the problems of entanglement, breakage and increased manufacturing costs of the methods and apparatus of the background art. Moreover, there is a need in the art for an OETO apparatus for unwinding yarns with anti-tack additives that can be implemented in a relatively small footprint.